The present invention relates to a puffer type gas-insulted circuit breaker for breaking or interrupting relatively large electric currents in a plant such as a transformer station, and, more particularly to an improvement in an insulated nozzle and an insulated cover disposed in the vicinity of a portion of a circuit breaker in which an arc occurs.
When a large electric current is interrupted by a circuit breaker of the above-described type, a high-temperature plasma arc occurs between a fixed or stationary contact and a movable contact, that is, between electrodes. The puffer type gas-insulated circuit breaker is adapted to extinguish the arc, by an insulating gas such as an SF6 gas blowing toward the arc. To this end, a cylindrical insulated nozzle having a throat portion is provided to surround the contact portion between the stationary movable electrodes. When either of the electrodes passes through the throat portion of the insulated nozzle as the electrodes are being separated, the gas of the above-described type flows through the throat portion toward the arc.
A circuit breaker of the type described above has been disclosed, for example, in Japanese Patent Unexamined Publication No. 60-212923 , wherein a substantially cylindrical insulated cover between the electrode and the insulated nozzle, the insulated cover and the insulated nozzle defining a gas passage therebetween and with the arc gas extinguishing passing through the gas passage.
The above-described insulated nozzle is usually made of a synthetic resin of electric insulation. However, there arises a case where, when an arc occurs at the time of current interruption, voids and carbon ar caused not only on the surface of the insulated nozzle but also in the inside thereof due to energy lines generated from the arc. In order to overcome this problem, Japanese Patent Publication No. 1-37822 proposes utilizing a filler of boron nitride power in a fluororesin for forming the nozzle to prevent the entrance of an arc thereinto.
Further, Japanese Patent Unexamined Publication No. 63-119121, corresponding to U.S. Pat. No. 4,791,256, has proposed an insulated nozzle for a circuit breaker, which is made of a fluororesin containing 0.3 to 1.0 wt % of boron nitride. Furthermore, in "KEY TECHNOLOGIES FOR DEVELOPING A 420 KV 50 KA GCB INTERRUPTER UNIT" 89 WM 077-9 PWRD, 1989 IEEE, description is made on pp.3 to 6 about a nozzle formed of PTFE in which a filler is mixed.